This invention relates in general to thermographic imaging systems and more particularly to improved processing temperature uniformity in heated drum processors for thermally processed thermographic imaging media.
Photothermography is an established imaging technology. In photothermography, a photosensitive media is exposed to radiation to create a latent image which can then be thermally processed to develop the latent image. Devices and methods for implementing this thermal development process are generally known and include contacting the imaged photosensitive media with a heated platen, drum or belt, blowing heated air onto the media, immersing the media in a heated inert liquid and exposing the media to radiant energy of a wavelength to which the media is not photosensitive, e.g., infrared. Of these conventional techniques, the use of heated drums is particularly common.
A common photosensitive media useable in these imaging processes is known as a photothermographic media, such as film and paper. One photothermographic media has a binder, silver halide, organic salt of silver (or other deducible, light-insensitive silver source), and a reducing agent for the silver ion. In the trade, these photothermographic media are known as dry silver media, including dry silver film.
In order to precisely heat exposed photothermographic media, including film and paper, it has been found to be desirable to use electrically heated drums. An apparatus employing this technique, a cylindrical drum is heated to a temperature near the desired development temperature of the photothermographic media. The photothermographic media is held in close proximity to the heated drum as the drum is rotated about its longitudinal axis. When the temperature of the surface of the heated drum is known, the portion of the circumference around which the photothermographic media is held in close proximity is known and the rate of rotation of the drum is known, the development time and temperature of the thermographic media can be determined. Generally, these parameters are optimized for the particular photothermographic media utilized and, possibly, for the application in which the photothermographic media is employed.
U.S. Pat. 5,580,478, issued Dec. 3, 1996, inventors Tanamachi et al., discloses a temperature controlled, electrically heated drum for developing exposed photothermographic media. A cylindrical drum has a surface and is rotatable on an axis. An electrical heater is thermally coupled to the surface of the cylindrical drum.
Separate electrical resistance heaters heat a central heat zone and contiguous edge zones.
The present medical imaging film used can draw relatively significant amounts of heat from the processor drum surface as it first contacts the drum and warms up. Current drum processors typically use a circumambient (circumferentially uniform) internal drum heater. Normal heating devices include resistive element blanket heaters attached to the drum or lamp type radiative devices located in the drum core. Circumambient heaters can cause locations of the drum to under heat and over heat when film enters the processor. In locations of early film contact, where the most significant heat load takes place, the drum temperature can decrease while in other locations the drum temperature can increase because it is not loaded as much. The temperature controller does not correct this. In a closed loop temperature control setup, the drum temperature can be controlled to a tight temperature variation at a location on the drum, but the overall drum temperature will still vary because of the non-even heat load as the film is applied to the drum. There is thus a need for an improved heated drum for processing media which has improved processing temperature and uniformity.
According to the present invention, there is provided a solution to the problems and a fulfillment of the needs discussed above.
According to a feature of the present invention, there is provided in a thermographic imaging system in which exposed thermographic imaging media is moved along a path, apparatus comprising; a movable member of thermally conductive material located along said path, said member having a first dimension parallel to said path and a second dimension perpendicular to said path, said member having a first side which thermally contacts media moved along said path and a second opposite side, a first electrical heater in thermal contact with said second side of said member; a second electrical heater in thermal contact with said second side of said member, said second electrical heater having a plurality of separately activated segments extending in said first dimension; and a control for selectively activating said segments as media is moved along said path into contiguity with each said segments.
The invention has the following advantages.
1. Improved processing temperature uniformity in thermographic imaging systems.
2. Improved media uniformity.